Marine anti-fouling coating formulations containing a soluble phase including a organotin polymer in combination with an insoluble phase including a crosslinked organotin polymer

ABSTRACT

A coating composition for marine structures containing a soluble acrylic organotin polymer and a soluble metal-free acrylic polymer, in combination with an insoluble crosslinked organotin polymer, and an insoluble filler in a coating composition solvent can provide a tough, durable flexible coating and can provide extended protection to marine structures from the growth or accumulation of marine organisms.

This invention was made with Government support under Contract.[.N0060-76-C-1002.]. .Iadd.N00600-76-C-1002 .Iaddend.awarded by theDepartment of the Navy. The Government has certain rights in theinvention.

FIELD OF THE INVENTION

The invention relates to containing compositions that can be applied tomarine structures such as ships, piers, oil drilling platforms,submerged pipelines, and others. The coating compositions of theinvention must form a film which can set and dry rapidly to a hard-toughbut flexible coating that is strongly bonded to the structure and canprevent the growth of accumulating of marine organisms by generating aneffective concentration of a biocide at the coating surface.

BACKGROUND OF THE INVENTION

The growth of marine organisms on structures exposed to fresh or saltwater is a problem having both practical and aesthetic aspects. Typicalmarine growth commonly involves both plants and animals such as seamoss, various forms of algae, acorn shells, goose muzzles, barnacles,tube worms, etc. Marine growth can be unsightly and can reduce theoperating efficiency of marine equipment such as heat exhangers, gates,dry docks, ships, pipelines, etc.

A major problem relates to marine growth on ships' hulls. Marineorganisms in substantial accumulations on ships' hulls can increase theenergy needed to propel a ship leading to either an increase in fuelconsumption or substantial reduction in ship speed. Marine organismsaccumulate on exposed hull surfaces at a rate such that they cannot beeconomically removed in dry dock.

One alternative which has been attempted in the past involves applyingto the ship's hull or other marine structure a coating that incorporatesa biocide which is slowly released at the surface of the coating to forma concentration lethal to the organism.

Useful marine anti-fouling coatings or paints must form a hard,flexible, relatively smooth film that can remain uncracked andunblistered for an extended period of time of up to five years or more.Further, during its useful life, the coating must provide an effectivemarine biocidal concentration of a biocidal composition at the surfaceof the coating that can prevent the accumulation or growth of marineorganisms.

Many such coatings have been proposed. The following is a discussion ofrepresentative types.

Sparman, U.S. Pat. No. 2,970,923 teaches essentially monomerictri-substituted methyl halides which can be used in coatingcompositions. James, U.K. Pat. No. 1,124,297 teaches an anti-foulingcoating composition comprising an organotin-containing polymer vehicleand a water soluble pigment which in combination can increase thebiocidal efficiency of the coating. Leebrick, U.S. Pat. No. 3,167,473teaches homopolymers and copolymers of trialkyl tin methacrylate in ananti-fouling coating composition containing a vinyl resin, an acrylicresin or an alkyd resin vehicle base, pigments, thickeners, fillers, ordriers blended in commonly available solvents. Hopewell, U.S. Pat. No.3,575,123 teaches hydrophilic acrylic resins made from a hydrophilicacrylic monomer containing in the polymer matrix essentially monomericorgano metallic compounds such as trialkyl tin halide, triaryl tinhalide, and others. Hopewell teaches that the hydrophilic acrylic resincan be crosslinked to reduce the resistance experienced by movingwatercraft. Dennington, U.S. Pat. No. 4,139,515 discloses an aqueousemulsion of a copolymer of a triorganotin salt of an olefinicallyunsaturated carboxylic acid and another unsaturated comonomer incombination with a substantially water insoluble metal containingpigment that is capable of reacting with sea water to form a watersoluble metal compound. Matsuda, U.S. Pat. No. 4,157,999 teaches a novelcopolymer containing copolymerized units of a substituted tin monomerand a specific aromatic monomer. DeGraff, U.S. Pat. No. 4,221,839teaches combining essentially monomeric toxic solid organo metalliccompounds with a water insoluble binder and a water soluble binder inorder to produce a coating composition which in response to themechanical action of the water, wears at a sufficient rate to release aneffective biocidal concentration of the organo metallic. Dawans, U.S.Pat. No. 4,262,097 teaches an organo metallic polymer composition whichis formed by grafting onto a main chain consisting of a chlorinatedpolymer, at least one chain of recurring units of an organotin monomer.Watanabe, U.S. Pat. No. 4,314,850 teaches an antifouling coatingcomposition containing an essentially monomeric triaryl tin compound, aresinous vehicle and an organic solvent.

In our developmental efforts we have found that by following thedirections of the prior art and forming anti-fouling coatingcompositions from a homopolymer or interpolymer of a trialkyl tinacrylate compound and blending the homopolymer or interpolymer with asolvent, vehicle, filler, thickener, or pigment, the resultingcompositions over an extended period of time either cannot form a hard,flexible, stable coating which can survive the marine environment orcannot provide an effective biocidal amount of trialkyl tin compound toprevent the growth or accumulation of marine organisms.

Accordingly, a substantial need exists for a coating composition whichcan be applied to marine surfaces that can survive intact in the marineenvironment without substantial cracking, blistering or peeling and canprovide an effective biocidal concentration of the trialkyl tin compoundat the surface of the coating for an extended period of time.

BRIEF DESCRIPTION OF THE INVENTION

We have found a marine coating composition that forms a tough, flexiblefilm, that has an extended lifetime in the marine environment and canrelease an effective amount of a marine biocide for a year or more,which comprises a coating composition solvent, ingredients which aresolvent soluble, and a portion which are solvent insoluble. The solubleingredients comprise an effective film-forming amount of a hydrophobicorganotin acrylic polymer composition, and a metal-free acrylic polymerfilm-forming agent. The insoluble ingredients comprise an effectivebiocidal amount of a solvent insoluble crosslinked organotin acrylicpolymer composition, an effective biocide-releasing amount of aninorganic filler composition. The preferred coating compositions of theinvention can also contain other components such as a pigment, a filler,a thickener, a binding agent, or mixtures thereof.

While we do not wish to be limited to a theory of action of theinvention, we believer that the hydrophobic film-forming organotinacrylic polymer in combination with a metal free acrylic film-formingpolymer provides a sufficiently tough, flexible film for the marineenvironment. The inorganic filler introduces a degree of porosity ororganotin availability to the film. The crosslinked organotin acrylicpolymer in combination with the organotin groups in the film-formingorganotin acrylic polymer acts to provide a sufficient loading oftriorganotin in the coating composition to maintain a high effectivebiocidal concentration on the marine coating surface for an extendedperiod of time. In this way .[.the.]. the solvent soluble and thesolvent insoluble components appear to interact in the coating toproduce a long wearing coating having an anti-fouling capacity superiorto prior coating compositions.

DETAILED DESCRIPTION OF THE INVENTION Film-Forming Organotin Polymer

The anti-fouling marine coating of the invention can contain ahydrophobic film-forming organotin polymer composition which is commonlya homopolymer or interpolymer of a monomer having an organotin group andolefinically unsaturated group or vinyl group. The organotin polymers ofthe invention are: (1) substantially hydrophobic and have fewhydrophilic groups in the polymers that would change the basichydrophobic film-forming nature of the composition; (2) efficient ingenerating an effective toxicant concentration of labile organotin atthe coating surface; and (3) alone or in combination with the metal-freeacrylic polymers, able to form a sufficiently tough, flexible film forthe marine environment. The organic substituents in the organotin groupcan be aliphatic, aromatic or unsaturated. Typical aliphatic groups cancontain 1 to 10 carbon atoms such as methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, t-butyl, amyl, 2-ethyl-hexyl, neooctyl, cyclohexyl,4-methyl-cyclohexyl, 2-chlorocyclohexyl, 2-nitro-cyclohexyl, 3-t-butylcyclohexyl, 2-methyl cyclohexyl, etc. The aliphatic groups may alsocontain other substituent groups that do not interfere with either thegeneration of a biocidal concentration of organotin at the coatingsurface, the polymerization of the tin-containing polymer or theblending of the anti-fouling coating preferred aliphatic groups contain2 to 5 carbon atoms, such as ethyl, n-propyl, isopropyl, n-butyl,t-butyl and amyl. The substituents can also be primary C₆₋₁₂ aryl, suchas phenyl, chlorophenyl, nitrophenyl, tolyl, xylyl, ethyl phenyl, etc.

Typical triorganotin containing polymers are homopolymers orinterpolymers of methacrylic, acrylic or vinyl monomers such astri-n-butyl tin acrylate, tri-n-propyl tin acrylate, tri-isopropyl tinacrylate, tri-isobutyl tin acrylate, tri-benzyl tin acrylate, ditertiarybutyl methyl tin acrylate, di-n-propyl ethyl tin acylate, tribenzyl tinacrylate, tri-n-butyl tin methacrylate, tri-n-propyl tin methacrylate,tri-isopropyl tin methacrylate, tri-tertiary-butyl tin methacrylate,triethyl tin acrylate, di-tertiary butyl ethyl tin methacrylate,di-n-propyl methyl tin methacrylate, tribenzyl tin methacrylate,tri-n-butyl tin adduct of vinyl alcohol, etc. or mixtures thereof. Thetin-containing polymers of this invention may also be an interpolymer ofone or more of the ethylenically unsaturated tri organotin containingmonomers and one or more of another ethylenically unsaturated comonomerfree of organotin groups. Commonly hydrophobic ethylenically unsaturatedcomonomers which can be used to prepare the interpolymer include acrylicmonomers such as methylacrylate, methylmethacrylate, ethylacrylate,acrylic acid, methacrylamide, acrylamide, acrylonitrile, and other vinylmonomers such as vinyl chloride, styrene, parachlorostyrene, vinylacetate, vinyl butyrate, dialkyl maliate, etc.

Preferred hydrophobic organotin-containing acrylic polymer compositionsare interpolymers or copolymers of a trialkyl tin acrylic or methacryliccompound and an acrylic monomer such as acrylic acid, methacrylic acid,methylacylate, methylmethacrylate, or mixtures thereof. Typically, thecomposition of the film-forming interpolymer contains about 30 to 50mole % of the ethylenically unsaturated tri-organotin-containing acrylicmonomer and about 50 to 70 mole % of the metal free acrylic monomer. Thepolymers have a molecular weight ranging between 26,000 and 100,000. Thealkyl substituents of the tri-organotin group include ethyl, propyl,isopropyl, n-butyl, isobutyl, tertiary butyl, or mixtures thereof. Themost preferred hydrophobic organo-tin-containing acrylic polymercompositions is a copolymer of tri-n-butyl tin methacrylate, andmethylmethacrylate wherein there are about 30 to 50 mole % tri-n-butyltin methacrylate, and 50 to 70 mole % methylmethacrylate. These polymershave a molecular weight ranging from about 45,000 to 70,000. Acommercial example of the most preferred film forming hydrophobicorganotin-containing acrylic polymer composition are the Biomet 300family of products of the M&T Corporation.

CROSSLINKED ORGANOTIN POLYMER

The hydrophobic insoluble crosslinked organotin polymeric compositionsare similar to the organotin polymers described above except they aresubstantially crosslinked. The hydrophobic crosslinked organotin speciesare crosslinked sufficiently to render them insoluble in the coatingcomposition solvent, are compatible with the film forming components ofthe coating composition, and have organotin groups which aresufficiently labile to aid in the generation of an effective toxicantconcentration at the coating surface. In addition they must exist in afinely divided particulate state which is sufficiently small to permitthe ready dispersion of the particles in the coating compositionsolvent.

The particles are most commonly in a particle size range of about 1 to250 microns. Preferably the particle size ranges from about 2 to 100microns and has a particle size distribution such that less than 0.5% ofthe particles are retained by a -200 mesh screen. Most preferably, forreasons of ease of preparation of the coating compositions and readyavailability of the oranotin compounds to diffusion from the coating,the particle size ranges from about 5 to 75 microns and has a particlesize distribution such that less than 0.2% of the material is retainedby -325 mesh screen.

The crosslinking of the resin results in a substantial increase in themolecular weight of the polymer matrix and results in a sharp reductionof the solubility of the crosslinked polymer molecules in coatingcomposition solvents. We have found that these insoluble crosslinkedspecies can be added to the coating composition to substantiallyincrease the available amount of organotin in the coating composition.The substantially increased organotin loading in the coatings insuresthat the coating composition can release a higher effective biocidalconcentration of organotin species at the coating surface for anextended period of time.

The crosslinked hydrophobic organotin polymeric compositions can beobtained by (1) attached organotin groups to a crosslinked polymer whichcontains active sites such as pendent hydroxy or carboxy groups or (2)polymerizing the tin-containing monomer with a crosslinking agent andoptionally other monomers. Typical crosslinked polymers are (1)copolymers and interpolymers prepared with styrene derivatives and across-linking agent; or (2) copolymers and interpolymers of acrylicacid, methacrylic acid, or mixtures thereof and a crosslinking agent.

The organic substituents of the organotin groups can be aliphatic,aromatic, or unsaturated. Typical aliphatic groups an contain 1 to 10carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl,iso-butyl, amyl, 2-ethylhexyl, neooctyl, cyclohexyl, 4-methylcyclohexyl,4-chlorocyclohexyl, 3-nitrocyclohexyl, 3-t-butyl cyclohexyl,2-methylcyclohexyl, etc. The aliphatic groups may also contain othersubstituents groups that either do not interfere with the generation ofthe biocidal organotin composition at the coating surface, thepolymerization of the crosslinked organo-tin-containing polymer, or theblending of the antifouling coatings. Preferred aliphatic groups contain2 to 5 carbon atoms such as ethyl, n-propyl, isopropyl, n-butyl,t-butyl, amyl, etc. The substituents can also be primarily C₆₋₁₈ arylsuch as phenyl, chlorophenyl, nitrophenyl, tolyl, xylyl, ethylphenyl,2-ethylhexylphenyl, nonylphenyl, etc. The preferred crosslinked polymersare copolymers and interpolymers of acrylic acid, methacrylic acid, ormixtures thereof and a crosslinking agent. These polymers may beprepared with comonomers which need not contribute active sites, such aspendent carboxy groups, to the polymer and need not contribute to thecrosslinking of the polymers.

Common ethylenically unsaturated comonomers which can be used includeacrylic monomers such as methylacrylate, methylmethacrylate,ethylacrylate, acrylic acid, methacrylamide, acrylamide, acrylonitrile,and other vinyl monomers such as vinyl chloride, styrene,parachlorostyrene, vinyl acetate, vinyl butyrate, dialkyl maleate, etc.

The important characteristic of the crosslinked polymer used in thisinvention is that they contain either a sufficient number of activesites to which organotin groups can be attached or sufficient organotinon the monomers used to form the crosslinked polymer, which provides forthe generation of an effective toxicant concentration, and aresufficiently crosslinked so that they are insoluble in the coatingcomposition solvent.

Crosslinking agents which can be used to prepare the crosslinkedorganotin-containing polymers contain 2 or more technically unsaturatedpolymerizable groups separated by a group of sufficient size to permitthe polymerizable group to be included in separate polymer chains.Commonly crosslinking agents are added to a polymerization mixture inproportions of from about 0.05 to 15 mole-%, preferably 0.1 to 5 mole %based on the polymerization mixture. Typical examples of effectiveethylenically unsaturated crosslinking agents include ethylene glycoldiacrylate, ethylene glycol dimethacrylate, 1,2-butylene glycoldimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycoldimethacrylate, 1,1,1-trimethylolpropane trimethacrylate, divinylbenzene, diallyl tartrate, diallyl maleate,N,N'-methylene-bis-acrylamide, ethylene glycol vinyl allyl citrate, andmany others known to those skilled in the art.

Preferred crosslinked hydrophobic organotin containing polymers are theproducts of the reaction of a trialkyltin compound with a crosslinkedcopolymer or interpolymer of methacrylic acid, acrylic acid, or mixturesthereof and a crosslinking agent. Typically, the crosslinked copolymeris prepared from 80 to 95 mole % acrylic monomer and 5 to 20 mole % ofthe crosslinking agent. The alkyl substituents on the tin are typicallyethyl, propyl, isopropyl, n-butyl, isobutyl, tertiary butyl, or mixturesthereof.

The most preferred crosslinked hydrophobic organotin containing polymeris the product of the reaction between bis(tri-n-butyl tin) oxide andthe crosslinked copolymer of methacrylic acid and divinyl benzenewherein the crosslinked copolymer is prepared from 87 to 93 mole %methacrylic acid and 7 to 13 mole % divinyl benzene. A commercialexample of the bis(tri-n-butyl tin) oxide of the Biomet TBTO family ofproducts of the M & T Corporation. A commercial example of thecrosslinked copolymer is the Amberlite IRC-50 family of products of theRohm & Haas Company.

METAL FREE FILM-FORMING RESIN

The film forming characteristics of the hydrophobic triorganotin acryliccomposition can be augmented by the use of commonly availablefilm-forming acrylic resins. These resins are similar to the organotinfilm-forming resin described above except that they are substantiallyfree of organotin groups. The resins that can be used to augment thefilm-forming capacity of the compositions of the invention aresubstantially hydrophobic resins made by polymerizing commonly availableethylenically unsaturated monomers such as acrylic monomers, vinylesters, vinyl halides, styrenes and other ethylenically unsaturatedmonomers. The monomer blend prior to polymerization should be adjustedso that the final polymer has substantial hydrophobic film-formingcapacity. Preferred resins used for augmenting the film-formingcapability of the invention include homopolymers and interpolymers ofalkyl acrylate and alkyl methacrylate monomers. Commonly the alkylgroups are methyl, ethyl, isopropyl, tertiary butyl, amyl, lauryl, etc.The molecular weight of the preferred film-forming copolymers range fromabout 50,000 to 100,000.

The most preferred resin for augmenting the film-forming characteristicsof the invention are butyl methacrylate polymers having a molecularweight of about 50,000 to 100,000. A commercial example of the mostpreferred resins for augmenting the film forming characteristics of theinvention are the Acryloid F-10 family of products of the Rohm and HaasCompany.

Substantially any nonaqueous solvent common in acrylic coatingformulations can also be used to form the anti-fouling compositions ofthe invention. Typical examples of aliphatic or aromatic, polar andnon-polar solvents include naptha, mineral spirits, acetone,methyisobutyl ketone, ethyl acetate, amyl acetate, methanol, ethanol,isopropanol, tertiary butanol, turpentine, benzene, cellosolve, etc. Andmixtures thereof.

The anti-fouling coating compositions of the invention can contain aninorganic filler which aids in film formation and can also aid ininsuring the ready availability of the triorganotin compound to thesurface of the coating composition. Typical inorganic fillers are.Iadd.clays .Iaddend.byorites, silica, and silicate compositions whichcan be dispersed in the coating composition solvent and which cancooperate with the hydrophobic triorganotin-containing acrylic and thefilm-forming acrylic in forming a hard durable marine coating. Typicalsilica or silicate fillers include silica (silicon dioxide), aluminumsilicate, calcium silicate, magnesium silicate, mixed metal silicates,etc. Further information regarding silica fillers which can be used inthe coatings of this invention can be found in Kirk-Othmer Encyclopediaof Chemical Technology, 2nd Edition, Volume 18, pp. 46-105, whichdiscloses a great deal of information regrading silica, amorphoussilica, vitreous silica, silicates and their associated properties.

The anti-fouling coating composition of the invention can also containthickeners such as commonly available clays and modified clays which canbe used to modify the viscosity of the composition in order to easeapplication. A commercial example is the Bentone family of products ofNL Industries, Inc. Information regarding clays and their uses can befound in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition,volume 5, pp. 541-586.

The anti-fouling coating compositions can also contain pigments whichcan aid in indicating the amount and location of the coatingcomposition, can aid in military camouflage and can aid in locating themarine structure. Such pigments can include titanium dioxide, blackferric oxide, carbon black, and others depending on the desired color.Further information regarding the nature and composition of otherpigment compositions can be found in Kirk-Othmer Encyclopedia ofChemical Technology, 2nd Edition, Volume 15, pp. 495-605.

The anti-fouling coating compositions of the invention can contain avariety of other compositions such as surfactants, perfumes,preservatives, anti-foam agents, etc. which aid in the blending,handling and application of the coating composition.

The anti-fouling coating compositions of the invention commonly containabout 8 to 28 parts of a film-forming hydrophobic tri-organotin acrylicpolymer, about 6 to 30 parts of the crosslinked hydrophobic organotinacrylate composition, about 3 to 24 parts of the inorganic fillercomposition, about 1 to 6 parts of the metal free film forming acrylicpolymer, and about 45 to 56 parts of the coating composition. Thepreferred anti-fouling coating compositions of the invention commonlycontain about 12 to 16 parts of the hydrophobic film-formingtriorganotin acrylic polymer, about 8 to 20 parts of the acrylichydrophobic crosslinked triorganotin acrylic composition, about 2 to 5parts of the tin free acrylic film-forming composition, about 5 to 22parts of the inorganic filler, and about 48 to 53 parts of the coatingcomposition solvent. The most preferred anti-fouling coating compositionof the invention contains about 10 to 15 parts of a hydrophobicorganotin copolymer of tri-n-butyl tin methacrylate, andmethylmethacrylate, about 8 to 9 parts of the acrylic hydrophobiccrosslinked tri-n-alkyl tin acrylic composition, about 3 to 4 parts of afilm-forming polymer of butylmethylmethacrylate, about 16 to 18 parts ofan inorganic silicate filler, and about 50 to 55 parts of a coatingcomposition solvent containing about 100 parts of mineral spirits withabout 1 to 10 parts of methanol. The most preferred anti-fouling coatingcompositions can contain about 1 to 3 parts of a clay thickener, andabout 1 to 4 parts of a pigment.

EXAMPLE 1

Into a number 2 Roalox mill jar was placed two quarts of small borundumgrinding media (cylinders having 3/8 inch O.D. and 3/8 in length) andtwo quarts of medium grinding media (cylinders 1/2 inch O.D. and 1/2 inlength). Into a separate number 3 Roalox mill jar was placed threequarts of small grinding media along with three quarts of mediumgrinding media. Into the number two jar was placed 75 grams of carbonblack, 264.0 grams of an insoluble tri-n-butyl tin containingcrosslinked resin made by reacting tri-n-butyl tin oxide with acopolymer of about 87 to 93 mole % methacrylic acid and 7 to 13 mole %of divinyl benzene, 528.0 grams of silica, 44.0 grams of a fumed silica,880.0 grams of a 45 wt. % solution in mineral spirits of a tincontaining acrylic polymer comprising a copolymer of tri-n-butyl tinmethacrylate and methamethacrylate having 50 mole % tin containingmonomer, 293.0 grams of a 40 wt. % solution in an aromatic naphthasolvent (90% mineral thinner and 10% ansco F.) homopolymer of butylmethacrylate having a molecular weight of about 75,000 and 441.0 gramsof mineral spirits. The identical ingredients were placed in the number3 Roalox jar except that the amounts were doubled. Into a separate 100mL container was place 22.0 grams of a bentonite clay (Bentone 38) and7.0 grams of 95 percent methanol. The mixture was blended until a pastewas formed and the mixture was placed in the number 2 Roalox mill jar.After the paste was added, the mill jar was closed and sealed. A drypaste containing bentonite clay and methanol was prepared as exactly asabove except that the amounts of the ingredients were exactly doubled.The dry paste was added to the #3 Roalox milljar. The mill jars wereclosed and sealed. Both Roalox were milled until the contents of themill jar attained a Hagman number 5 fineness of grind (about 72 hours).The mill jars were opened and the resulting composition was emptied fromeach jar into a suitable container, retaining the grinding media in eachjar. Into the number 2 Roalox jar was placed 500 grams of mineralspirits and into the number 3 Roalox was placed 1,000 grams of mineralspirits. The jars were rinsed with the mineral spirits and the contentsof the jars and the coating compositions were combined and mixed until auniform well disposed coating composition was formed.

Coating compositions of the Examples were tested on cold rolled steelpanels having dimensions of 1/8 inch thickness, 10 inch width, 12 inchlength with a 1/4 inch hole, 1 inch from 174 and a 1 inch hole centeredalong the top 10 inch edge. The panels were primed and two primed panelswere coated with a 2 to 4 mill dry film of the coatings Examples Ithrough IV.

The coatings of the application were also applied in stripes on shipshulls from the water line to the keel. The ships were operated in thePacific and Indian Oceans, in the Atlantic Ocean and in theMediterranean Sea in the ordinary course of naval operation. The resultsof the testing of the coated panels and ships is shown in Tables II andIII.

                  TABLE I                                                         ______________________________________                                        The method of Example I was repeated except that                              the following amounts of ingredients were substituted                         for the ingredients recited in Example I.                                            Example II                                                                              Example III Example IV                                              #2 Jar                                                                              #3 Jar  #2 Jar  #3 Jar                                                                              #2 Jar                                                                              #3 Jar                               ______________________________________                                        Carbon   75      150     80    160   15.6  31.2                               Black                                                                         Insoluble                                                                              340     680     418   836   780   1560                               Tin Con-                                                                      taining                                                                       Resin                                                                         Silica   510     1020    501   1004  117   234                                Cabosil  20      40      25    50    --    --                                 (silica-                                                                      fumed)                                                                        Bentonite                                                                              21.25   42.5    21    42    19.5  39                                 (Clay)                                                                        Soluble  850     1700    864   1728  1014  2028                               Tin Con-                                                                      taining                                                                       Resin*                                                                        Soluble Film                                                                           283     566     209   418   195   390                                Forming                                                                       Metal                                                                         Free                                                                          Resin**                                                                       Mineral  910     1820    945   1890  516   1032                               Spirits                                                                       Methanol 8.5     17.0    7     14    7.8   15.6                               (95%)                                                                         Xylol*** --      --      --    --    40    80                                 Methyl-n-                                                                              --      --      --    --    117   234                                butyl                                                                         Keton***                                                                      ______________________________________                                         *45 wt. % in mineral spirits                                                  **40 wt. % in aromatic naphtha solvent                                        ***Added with mineral spirits                                            

                                      TABLE II                                    __________________________________________________________________________    PANEL TEST OF COATINGS                                                        Example No.                                                                            IV  IV  IV    I   I   I     IV  I   IV  I                            __________________________________________________________________________    Number of                                                                               1   1   1     1   1   1     1   1   1   1                           Panels                                                                        Site     Miami                                                                             Pearl                                                                             Annapolis                                                                           Miami                                                                             Pearl                                                                             Annapolis                                                                           Pearl                                                                             Pearl                                                                             Pearl                                                                             Pearl                        Film     2 to 3                                                                            2 to 3                                                                             4    2 to 3                                                                            2 to 3                                                                             4     4   4   4   4                           thickness                                                                     (mil)                                                                         Total Fouling                                                                 resistance (% free                                                            of fouling) @                                                                 6 mos.   100 100 100   100 100 100   100 100 100 100                          12 mos.  100 100 100   100 100 100   100 100 100 Lost                         18 mos.  100  95 100   100 100 100   100 100 100                              24 mos.  100  80 100   100 100 100   100 100 --                               30 mos.  100 eroded                                                                            100   Lost                                                                              eroded                                                                            100   100 --  --                               36 mos.  Lost    100           100   --  --  --                               42 mos.          100           100   --  --  --                               46 mos.          --            --    --  --  --                               52 mos.          100           100   100 100 100                              __________________________________________________________________________

                  TABLE III                                                       ______________________________________                                        SHIP TEST OF COATINGS                                                         WATER LINE TO KEEL STRIDE                                                     Example No.                                                                           IV        I                                                                   USS       USS       IV       I                                                OUEL-     OUEL-     USS      USS                                      Ship Name                                                                             LETTE     LETTE     INGRAM   INGRAM                                   Stripe #                                                                              1      2      1    2    1     2    1    2                             ______________________________________                                        Area of 100    100       100  100   100  100  100                             Test                                                                          Stripe                                                                        (ft.sup.2)                                                                    ______________________________________                                    

We have found that the ratio, in the most preferred compositions,between the amount of soluble tin containing resin and the amount of theinsoluble tin containing resin, and the ratio between the total amountof tin containing resin (soluble and insoluble) and the nontoxic bindermaterials (the tin-free acrylic resins) are important to forming a highperformance coating composition. We have also found that, in the mostpreferred compositions, the type and amount of inorganic filler isimportant to insure the effective diffusion of sufficient tin compoundto the surface of the coating to produce a sufficient bioavailableamount of toxic tin compound. The ratio of the amount of soluble tincontaining resin to insoluble tin containing resin is about 0.5 to 1.8parts by weight of the soluble tin containing resin per each part byweight .[.by.]. .Iadd.of .Iaddend.the insoluble tin containing resin.The ratio of tin containing resin (both soluble and insoluble) to metalfree resin is about 5 to 16 parts by weight of the tin containing resinsper each part by weight of the metal free resin. The amount of silica inthe coating can range from about 4 to 18 weight percent.

The anti-fouling coating compositions of the invention are commonlycompounded using commonly available mixing equipment. While the order ofaddition of components is not critical, typically the organic and theinorganic constituents of the coating composition are added to a mixerfollowed by the solvent. The blending equipment is operated until themixture obtains a uniform appearance and the coating composition can bewithdrawn from the mixing equipment and drummed.

The fully compounded anti-fouling coating compositions of the inventiontypically contain about 8.5 to 9.5 lbs. of coating composition pergallon, has a viscosity according to Federal Standard 141-A Method 4281of about 50 to 100 KU, a tin content based on solids of about 5 to 25wt-%, and can be applied at a rate such that the final dry filmthickness ranges from about 1 to 15 mils or more. Commonly the coatingcompositions of the invention can be applied to generally metallicsurfaces with a sprayer, a brush or a roller.

An examination of the data recorded in Tables II and III reveals thatthe novel, unique coating composition prepared in the Examples canprovide protection to ships bottoms in the marine environment and canprevent fouling (85% to 100% resistance to fouling) for up to six years.Applicant's coating compositions were tested along with coatingcompositions made by others from tri-n-alkyl-methacrylate containingcoating compositions prepared by others. However, we understand, fromthe navy, that only the coating compositions disclosed in thisapplication produced a hard-tough coating that could provide resistanceto fouling for more than one year.

The above specification Examples and data are provided to illustrate andto promote an understanding of the invention. However, since manyembodiments of the invention can be made without departing from thespirit .[.of.]. .Iadd.or .Iaddend.the scope of the invention, theinvention resides in the claims hereinafter appended.

We claim:
 1. A coating composition that can be applied to marine surfaces to form a durable, tough, flexible film and can release an effective amount of a marine biocide, which comprises:(a) an effective amount of a coating composition solvent; (b) a portion soluble in the solvent comprising an effective biocidal amount of a film-forming organotin acrylic polymer composition and an effective film-forming amount of a metal-free acrylic polymer composition and; (c) portion insoluble in the solvent comprising an effective biocidal amount of a crosslinked organotin acrylic polymer composition having sufficiently small suspendable particle size and an effective biocide releasing amount of an inorganic filler .Iadd.selected from the group consisting of a byorite, a silica, a silicate, a clay, or a mixture thereof.Iaddend..
 2. The coating composition of claim 1 wherein the film-forming organotin acrylic polymer composition comprises an interpolymer of an acrylic monomer and .[.an.]. .Iadd.a .Iaddend.trialkyl tin acrylic monomer.
 3. The coating composition of claim 2 wherein the trialkyl tin acrylic monomer is a trialkyl tin methacrylate.
 4. The coating composition of claim 3 wherein the trialkyl tin methacrylate is tri-n-butyl tin methacrylate.
 5. The coating composition of claim 1 wherein the metal-free acrylic polymer composition is a homopolymer or interpolymer of butyl methacrylate, isobutyl methacrylate, methylmethacrylate, or mixtures thereof.
 6. The coating composition of claim 1 which also contains a pigment, a thickener, or mixtures thereof.
 7. The coating composition of claim 6 wherein the pigment comprises a black iron oxide, carbon black, or mixtures thereof.
 8. The coating composition of claim 6 wherein the thickener is a clay-type thickener.
 9. The coating composition of claim 1 wherein the coating composition solvent comprises an aliphatic solvent, a ketone solvent, an alcohol solvent, an aromatic solvent, or mixtures thereof.
 10. A marine structure having a durable, tough, flexible film that can release an effective amount of a marine biocide for a year or more wherein the film comprises:(a) in a continuous phase, an effective film-forming, biocidal amount of a hydrophobic organotin acrylic polymer composition, and a film-forming metal-free acrylic polymer composition; and (b) dispersed in the continuous phase an effective biocidal amount of .[.a.]. discrete particles having a sufficiently small dispersable particle size of a crosslinked organotin acrylic composition and an effective biocide releasing amount discrete particles of an inorganic filler .Iadd.selected from the group consisting of a byorite, a silica, a silicate, a clay, or a mixture thereof.Iaddend..
 11. The structure of claim 10 wherein the organotin acrylic polymer composition comprises an interpolymer of an acrylic monomer and an trialkyl tin acrylic monomer.
 12. The coating composition of claim 11 wherein the trialkyl tin acrylic monomer is a trialkyl tin methacrylate.
 13. The coating composition of claim 12 wherein the trialkyl tin methacrylate is tri-n-butyl tin methacrylate.
 14. The coating composition of claim 10 wherein the metal-free acrylic polymer composition is a homopolymer or interpolymer of butyl methacrylate, isobutyl methacrylate, methylmethacrylate, or mixture thereof.
 15. The coating composition of claim 10 which also contains a pigment, a .[.thickner.]. .Iadd.thickener.Iaddend., or mixtures thereof.
 16. The coating composition of claim 15 wherein the pigment comprises a black iron oxide.[.,.]. or carbon black.[.,.]..
 17. The coating composition of claim 15 wherein the .[.thickner.]. .Iadd.thickener .Iaddend. is a clay-type .[.thickner.]. .Iadd.thickener.Iaddend..
 18. A method of inhibiting marine growth which comprises applying the coating composition of claim 1 to a surface exposed to the marine environment.
 19. A coating composition that can be applied to marine surfaces to form a durable, tough, flexible film and can release an effective amount of a marine biocide, which comprises:(a) about 45 to 56 parts of a coating composition solvent; (b) a portion soluble in the solvent comprising about 8 to 28 parts of a film-forming hydrophobic triorganotin acrylic polymer and about 1 to 6 parts of a metal-free film-forming acrylic polymer; and (c) a portion insoluble in the solvent comprising about 6 to 30 parts of the crosslinked organotin acrylic polymer composition having a particle size of about 1 to 250 microns and about 3 to 24 parts of .[.the inorganic filler composition.]. .Iadd.an inorganic filler selected from the group consisting of a byorite, a silica, a silicate, a clay, or a mixture thereof.Iaddend.: each component present per one hundred parts of the coating composition.
 20. The composition of claim 19 wherein the coating composition solvent comprises mineral spirits and the inorganic filler comprises a silicate, a clay, .[.a carbon black.]. or mixtures thereof.
 21. A coating composition that can be applied to marine surfaces to form a durable, tough, flexible film and can release an effective amount of a marine biocide, which comprises:(a) about 48 to 53 parts of the coating composition solvent; (b) a portion soluble in the solvent comprising 12 to 16 parts of a hydrophobic film-forming tri-n-butyl tin acrylic polymer, about 2 to 5 parts of the tin-free acrylic film-forming composition; and (c) a portion insoluble in the solvent comprising about 8 to 20 parts of a crosslinked tri-n-butyl tin acrylic composition and about 5 to 22 parts of an .[.organic.]. .Iadd.inorganic .Iaddend.filler .Iadd.selected from the group consisting of a byorite, a silica, a silicate, a clay, or mixtures thereof.Iaddend.; each component present per one hundred parts of the coating composition.
 22. The composition of claim 21 wherein the coating composition solvent comprises mineral spirits, methanol or mixtures thereof.
 23. The composition of claim 21 wherein the inorganic filler comprises a clay, a silica, .[.carbon black,.]. or mixtures thereof.
 24. A coating composition that can be applied to marine surfaces to form a durable, tough, flexible film and can release an effective amount of marine biocide, which comprises:(a) an effective amount of a coating composition solvent comprising a mixture of mineral spirits and methanol; (b) a portion soluble in the solvent comprising about 10 to 15 parts of a copolymer of tri-n-butyl tin methacrylate and methyl methacrylate and about 3 to 4 parts of a film-forming methyl methacrylate; and (c) a portion insoluble in the solvent comprising a hydrophobic crosslinked tri-n-butyl tin acrylic composition; about 16 to 18 parts of an inorganic silicate filler; about 1 to 3 parts of a clay thickener and about 1 to 4 parts of carbon black; each component present per one hundred parts of the coating composition. 